Such preforms are produced in the injection molding process with the aim of blowing from them--in a later process step of a subsequent hollow blast process--hollow body such as, for example, a plastic bottle, a plastic container or the like. In order, therefore, to produce such a preform in the injection molding process there is required in a manner known per se an injection molding machine which essentially consists of two mold halves movable with respect to one another, in which the one mold half which is connected to an extruder injects corresponding hot-fluid plastic material into the mold half, after which then the mold half is cooled and the preform is now present in the injection molding machine in the allocated mold core.
In order properly to cool such a still very hot preform, it is a known practice to remove the preform from the injection molding machine and to bring it into a so-called after-cooling plate. In the after-cooling in the after-cooling plate, it is a known practice to receive the preform in corresponding cooled cavities of the after-cooling plate and to cool this preform at least on its outer circumference. As cooling agent there is used here in particular a liquid cooling medium such as, for example, water, oil or the like. It is also possible, however to use cooled air.
With this after-cooling of the preform in the after-cooling plate there is present, however, the disadvantage that the preform is only insufficiently cooled, because precisely the cooling performance in this after-cooling process is limited. As stated, the cooling occurs only on the outer circumference of the preform, which leads to the result that a temperature gradient arises in the direction of the interior space of the preform, which leads to a deterioration of the plastic material. Namely, in such an after-cooling, the plastic material tends toward a transformation of the crystal structure into the crystalline structure form, which severely impairs the quality of the preform. In the subsequent hollow blast process the preform, therefore can be further processed only with difficulty and with losses of quality.